1. Field of the Invention
The present invention relates to a novel method for producing a photocured image structure. More particularly, the present invention is concerned with a method for producing a photocured image structure by contacting a selectively photocured elastomer composition layer with a specific developer, thereby obtaining a photocured image structure, which method can be used for producing a photocured image structure while minimizing the swelling of the photocured image structure and without the danger of breakage of the photocured image structure and the danger of the formation of stains (known as "orange peel") on the photocured image structure. The photocured image structure obtained by the method of the present invention is especially suitable for use as a flexographic printing plate.
2. Discussion of the Related Art
Production of a photocured image structure from a photocurable elastomer composition is conducted by imagewise exposing a photocurable elastomer composition layer to actinic rays through an image-bearing transparency and then contacting the exposed, imagewise photocured composition layer with a solvent (developer) capable of dissolving the unexposed (uncured) portion of the exposed composition layer, to thereby wash-out the uncured portion and develop the photocured image portion.
In general, as a photocurable elastomer composition for producing a flexographic printing plate, a composition comprising, as the main ingredients, (a) a diene polymer, (b) an ethylenically unsaturated compound and (c) a photopolymerization initiator, is utilized. In the case of such a composition, the washing-out of the uncured portion after imagewise exposure cannot be performed by means of water or an aqueous solvent since the diene polymer as one of the main ingredients is insoluble in any of water and an aqueous solvent. Therefore, in the case of such a composition, the washing-out of the uncured portion has conventionally been conducted by using, as a developer, a chlorine-containing organic solvent, such as perchloroethylene and 1,1,1-trichloroethane, singly or in combination with an alcohol.
These chlorine-containing organic solvents are advantageous from the viewpoint of safety in handling, due to their inflammability. However, these chlorine-containing organic solvents pose great health problems since these solvents are very toxic to the human body. Moreover, these chlorine-containing organic solvents are known cause destruction of the protective ozone layer surrounding the earth. Therefore, a developing solvent which contains no chlorine has been desired from the viewpoint of improving the working environment and of the prevention of air pollution and environmental destruction.
Further, when a chlorine-containing solvent is used as a developer, not only is disadvantageously great the swelling of the photocured image structure produced by photocuring a photocurable elastomer composition, so that it takes a long drying time for the swollen image structure to recover its original dimensions, but also the photocured image structure is likely to be broken especially in relief portions corresponding to fine lines or small dots and stains known as "orange peel" are likely to be formed on the relief structure during the drying. Thus, a method in which use is made of a developing solvent which is free from the problems accompanying the chlorine-containing solvent and is improved in performance, has been desired.